This application is based on and hereby claims priority to European Patent Application No. 01109036.2, filed Apr. 11, 2001, the contents of which are hereby incorporated by reference.
The invention relates to a gas turbine having a number of rotor blades in each case combined into rows of rotor blades and arranged on a turbine shaft, and having a number of stator blades in each case combined into rows of stator blades and connected to a turbine casing.
Gas turbines are used in many areas to drive generators or working machines. Here, the energy content of a fuel is used to produce a rotational movement of a turbine shaft. To this end, the fuel is burned in a combustion chamber, compressed air being fed in from an air compressor. The working medium produced in the combustion chamber by the combustion of the fuel and under high pressure and at a high temperature is in this case guided via a turbine unit connected downstream of the combustion chamber, where it is expanded and produces power.
In order to produce the rotational movement of the turbine shaft, in this case a number of rotor blades usually combined into groups of blades or rows of blades are arranged on said turbine shaft, and drive the turbine shaft via a transfer of momentum from the working medium. In order to guide the working medium in the turbine unit, rows of stator blades connected to the turbine housing are additionally normally arranged between adjacent rows of rotor blades.
In the design of gas turbines of this type, in addition to the achievable output, a particularly high efficiency is usually a design objective. On thermodynamic grounds, an increase in the efficiency can in principle be achieved by increasing the outlet temperature at which the working medium flows out of the combustion chamber and into the turbine unit. Therefore, temperatures of about 1200xc2x0 C. to 1300xc2x0 C. are aimed at for such gas turbines and are also achieved.
At such high temperatures of the working medium, however, the components exposed to the latter are subjected to high thermal stresses. In order nevertheless, with high reliability, to ensure a comparatively long life time of the components involved, cooling of the components involved, in particular of rotor blades and/or stator blades in the turbine unit, is usually provided. The turbine blades are therefore normally designed such that they can be cooled, the intention being in particular to ensure effective and reliable cooling of the first rows of blades as viewed in the flow direction of the working medium. For the purpose of cooling, the respective turbine blade in this case normally has a coolant duct integrated into the leaf of the blade or the profile of the blade, from which duct a coolant can specifically be fed in, in particular to the thermally stressed zones of the turbine blades.
The coolant used in this case is normally cooling air. This is normally fed to the respective turbine blade via an integrated coolant duct, in the manner of open cooling. Starting from said coolant duct, the cooling air flows through the respectively provided areas of the turbine blade in branching ducts. On the outlet side, these ducts are left open, so that after passing through the turbine blade, the cooling air emerges from the latter and in the process is mixed with the working medium guided in the turbine unit.
In this way, a reliable cooling system for the turbine blades can be provided with comparatively simple means, it being possible even for thermally particularly stressed zones of the turbine blades to be acted on with coolant in a suitable way. On the other hand, however, at the introduction of the cooling air into the working medium guided in the turbine unit, care must be taken that its characteristic parameters, such as pressure and temperature, can be combined with or are compatible with the corresponding parameters of the working medium. In particular, the permissible heating of the cooling air during the cooling of the turbine blades is only limited, so that precisely in the case of comparatively high intended outlet temperatures of the working medium, a particularly large quantity of cooling air is required. This in turn has a limiting effect on the efficiency of the gas turbine.
The invention is therefore based on the object of specifying a gas turbine of the type mentioned above in which, with reliable cooling of the turbine blades with simple means, a particularly high efficiency can be reached.
According to the invention, this object is achieved in that at least some of the stator blades have an inlet for a cooling medium at their free end facing the turbine shaft.
In this case, the invention is based on the consideration that the gas turbine should be designed for a particularly high efficiency in such a way that reliable cooling of the turbine blades can be carried out with only a low quantity of cooling medium. For this purpose, the cooling of the turbine blades should be carried out in the manner of closed cooling, in which, after flowing through the turbine blade to be cooled, the cooling medium is not mixed with the working medium flowing in the turbine unit but, instead, is led away in a controlled manner and supplied to another use. This is because, in such a cooling concept, no adaptation to the working medium of the operating parameters of the cooling medium flowing away out of the turbine blades is required.
In order to keep particularly low the production and development expenditure for a gas turbine having cooled turbine blades closed in this way, the design should to a large extent follow the design of a gas turbine with open cooling of the turbine blades. The flow paths of the cooling medium in the gas turbine should approximate as far as possible to the flow paths of the cooling medium with open cooling even in the case of closed cooling. This can be achieved in a particularly simple way by the feeding of the rotor blades with cooling air via the turbine shaft and the blade root being maintained but the discharge of the cooling medium from the respective rotor blade being carried out in the manner of closed cooling, likewise through the blade root and into the turbine shaft. From there, the further discharge of the cooling medium is provided via a stator blade adjacent to the respective rotor blades, as viewed in the flow direction of the working medium. To this end, the respective stator blade has an inlet for the cooling medium at its free end facing the turbine shaft. During operation, the respective stator blade therefore has cooling medium flowing through it from its free end in the direction of its blade root in the manner of xe2x80x9ccountercurrentxe2x80x9d flow.
For a particularly beneficial saving effect with regard to the cooling medium needed, and therefore for a particularly high contribution to the increase in efficiency, such closed cooling is expediently provided for the first row of rotor blades, as viewed in the flow direction of the working medium. For this purpose, in an advantageous refinement, those stator blades which form the row of stator blades connected downstream of this row of rotor blades, as viewed in the flow direction of the working medium, have an inlet for the cooling medium at their free end.
On account of the envisaged flow direction of the cooling medium through the respective stator blades, the cooling medium flows out of the respective stator blades into an area of the turbine casing. The cooling medium can therefore be guided away particularly simply in a controlled manner. Accordingly, a gas turbine is in principle suitable both for the use of cooling vapor and also for the use of cooling air as the cooling medium. In this case, cooling air is advantageously provided as cooling medium. On the outlet side, said cooling air can be guided in an area of the front hook of the stator blade and, from there, can be supplied to the combustion again through holes in the stator blade carrier.
In order to provide closed cooling for the rotor blades forming the first row of rotor blades, as viewed in the flow direction of the working medium, in an advantageous development these rotor blades respectively have an integrated coolant duct, whose inlet and outlet is in each case arranged on the turbine shaft. A meander is in each case provided within the respective rotor blade as a flow path for the cooling medium. After flowing away out of the respective rotor blade, the flow path of the cooling medium proceeds radially outward through the stator blade respectively connected downstream. In such a configuration, both for the rotor blades and for the stator blades, a supply of cooling medium is carried out on their side respectively facing the turbine shaft. The cooling medium therefore flows into the respective rotor or stator blade in the comparatively hottest area, so that a particularly beneficial cooling action is achieved.
In a further advantageous refinement, the outflows of the coolant ducts of the respective rotor blades communicate with an antechamber which is integrated into the turbine shaft and which, in turn, on the outlet side is connected respectively to a coolant inlet of each of the stator blades belonging to the following row of stator blades, as viewed in the flow direction of the working medium.
In order to ensure particularly reliable flow of the cooling medium both through the respective rotor blades and through the stator blades in each case connected downstream on the coolant side, in a further advantageous refinement a compressor is connected into the flow path of the cooling medium, before its entry into the coolant ducts. Said compressor is expediently defined for a pressure increase in the cooling medium of about 0.5 to 1 bar. Here, the compressor can be configured as an axial compressor or else as a radial compressor. In the case of a configuration as a radial compressor, the pressure increase in the cooling medium can be achieved by means of an appropriately selected radial height of the holes in the rotating turbine shaft, use being made of the centrifugal force of the rotating turbine shaft to increase the pressure.
The advantages achieved by the invention consist in particular in the fact that, by means of the stator blades provided with an inlet for the cooling medium at their free end facing the turbine shaft and therefore flowed through radially from the turbine shaft outward toward the turbine casing, closed cooling of rotor blades is made possible in a manner particularly closely following existing open cooling concepts. Here, the flow path of the cooling medium in this closed cooling is kept particularly short, so that the pressure losses which occur are kept particularly low. Therefore, in a particularly simple way, closed cooling for the respective rotor blades can be achieved, in addition the cooling medium finally flowing out of the respective stator blades arising in the area of the turbine casing and therefore in a fixed location. Disposal of the cooling medium is therefore made possible in a particularly simple way.